The present description pertains to ventilator devices used to provide breathing assistance. Modern ventilator technologies commonly employ positive pressure to assist patient ventilation. For example, after determining a patient-initiated or timed trigger, the ventilator delivers a specified gas mixture into an inhalation airway connected to the patient to track a specified desired pressure or flow trajectory, causing or assisting the patient's lungs to fill. Upon reaching the end of the inspiration, the added support is removed and the patient is allowed to passively exhale and the ventilator controls the gas flow through the system to maintain a designated airway pressure level (PEEP) during the exhalation phase. Other types of ventilators are non-triggered, and mandate a specified breathing pattern regardless of patient effort.
Modern ventilators typically include microprocessors or other controllers that employ various control schemes. These control schemes are used to command a pneumatic system (e.g., valves) that regulates the flow rates of breathing gases to and from the patient. Closed-loop control is often employed, using data from pressure/flow sensors.
Many therapeutic settings involve the potential for leaks occurring at various locations on the ventilator device. The magnitude of these leaks can vary from setting to setting, and/or dynamically within a particular setting, dependent upon a host of variables. Leaks can impair triggering (transition into inhalation phase) and cycling (transition into exhalation phase) of the ventilator; and thus cause problems with patient-device synchrony; undesirably increase patient breathing work; degrade advisory information available to treatment providers; and/or otherwise comprise the desired respiratory therapy.
Determining Ventilator Leakage from Data Taken During a Stable Period within a Breath
This disclosure describes systems and methods for compensating for leaks in a ventilation system based on data obtained during periods within a breath in which the patient is neither inhaling nor exhaling. The methods and systems described herein more accurately and quickly identify changes in leakage. This information is then to estimate leakage later in the same breath or in subsequent breaths to calculate a more accurate estimate of instantaneous leakage based on current conditions. The estimated leakage is then used to compensate for the leak flow rates, reduce the patient's work of breathing and increase the patient's comfort (patient-ventilator breath phase transition synchrony). Without the improvements provided by the disclosed methods and systems, changes in the leak conditions during a breath may not be identified and/or accurately characterized until the following breath or later.
In part, this disclosure describes a method for identifying leakage in a respiratory gas supply system. In the method, data indicative of at least one of pressure and flow in the respiratory gas supply system is monitored during the delivery of respiratory gas to a patient. The method includes identifying that the data meet at least one stability criterion indicating that pressure and flow conditions have been stable for a period of time within a breath. These stability criteria are selected to identify stable periods within a breath in which the patient is neither inhaling nor exhaling. Upon identification of a stable period, the method calculates leakage information based at least in part on the data taken during the period of time within the breath. This leakage information may take the form of one or more orifice constants, leak conductances, leak factors, exponents, or other leak characteristics as required by the leakage model utilized by the ventilator to estimate instantaneous leakage from the current status (e.g., pressure or flow) of the ventilator. The method then uses the leakage information to determine a leakage rate in subsequent calculations performed after the stable period. This may include estimating an instantaneous leakage after the period of time based at least in part on the leakage information derived from data taken during the stable period.
This disclosure also describes a respiratory gas supply system that identifies stable periods within a breath and derives leakage information for use later in the same breath or in subsequent breaths in estimating instantaneous leakage. The system includes a pressure generating system capable of controlling the flow of breathing gas through a patient circuit and a patient interface to a patient, a stable period identification module that identifies a stable period within a breath, and a leak compensation module that calculates leakage information using data obtained during the stable period identified by the stable period identification module and that calculates, during subsequent stable and unstable periods within the breath or a later breath, an instantaneous leakage rate based on the leakage information.
This disclosure also describes another method for determining leakage from a respiratory gas supply system providing respiratory gas to a breathing patient. The method includes identifying at least one stable period within a patient breath and calculating leakage information based on pressure and flow data obtained during the at least one stable period. The method also, at times subsequent to the stable period, estimates the leakage from the respiratory gas supply system based on the leakage information calculated from the data obtained during the at least one stable period and the current data.
These and various other features as well as advantages which characterize the systems and methods described herein will be apparent from a reading of the following detailed description and a review of the associated drawings. Additional features are set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the technology. The benefits and features of the technology will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.